A smartphone, tablet, or other mobile computing device may be connected to the head unit of a car's audio/visual system or other vehicle computing device. The head unit may need to authenticate any smartphone that connects to it, to ensure that the smartphone is authorized to connect to and interact with the head unit. This may be done by issuing every smartphone, tablet, or other mobile computing device its own unique certificate. Issuing a unique certificate to every authorized mobile computing device may prevent certificates from being stolen and used on any other authorized or non-authorized mobile computing devices. The number of certificates required to ensure that every mobile computing device may be very large, and it may difficult to generate unique signatures for that many certificates.